AWS Cycle ASG
Background
When we change the launch profile, or we want to roll out a new version of the application, we need to cycle instances in an ASG.
This can be done in two ways.
Rolling update
Basically you roll one instance at a time. As each instance takes a long time (default 300s) to drain from ELB, if you have a lot of instances in the ASG, it can take a long time.
Blue/green deployment
In this way, you basically double the ASG, and then terminate old ones in one go. It's much more efficient.
How does it work
- Double ASG max-size and desired-size
- Wait for all instances to come into service
- Detach old instances from ASG and ELB
- Terminate old instances
- Scale back
How to use
./aws-cycle-asg -a asg_name -r aws_region -d detach_timeout
Default value:
aws_region: ap-southeast-2
detach_timeout: 300
Detach timeout can be found in the attribute Deregistration delay in the Target Group.